disk: convert part_* files to COBJ-$(CONFIG_XXX) style

Move the CONFIG_XXX out of the part_XXX.c file and into Makefile to
avoid pointless compiles.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/disk/part_amiga.c b/disk/part_amiga.c
index 6c3d748..c2daf6a 100644
--- a/disk/part_amiga.c
+++ b/disk/part_amiga.c
@@ -26,11 +26,11 @@
 #include <ide.h>
 #include "part_amiga.h"
 
-#if (defined(CONFIG_CMD_IDE) || \
-     defined(CONFIG_CMD_SCSI) || \
-     defined(CONFIG_CMD_USB) || \
-     defined(CONFIG_MMC) || \
-     defined(CONFIG_SYSTEMACE) ) && defined(CONFIG_AMIGA_PARTITION)
+#if defined(CONFIG_CMD_IDE) || \
+    defined(CONFIG_CMD_SCSI) || \
+    defined(CONFIG_CMD_USB) || \
+    defined(CONFIG_MMC) || \
+    defined(CONFIG_SYSTEMACE)
 
 #undef AMIGA_DEBUG